1. Field of the Invention
The present invention relates to a mobile computer device capable of carrying out communications while moving among a plurality of inter-connected networks, a computer management device for managing an address of the mobile computer, and a mobile computer device for carrying out cipher communications with the mobile computer, as well as a mobile communication method suitable for these devices.
2. Description of the Background Art
In conjunction with availability of computer systems in smaller sizes and lower costs and more enriched network environments, the use of computer systems has been rapidly expanded into a variety of fields, and there is also a transition from centralized systems to distributed systems. In this regard, in recent years, because of the advance and spread of the computer network technology in addition to the progress and improved performance of the computer system itself, it has become possible to realize not only a sharing of resources such as files and printers within an office but also communications (electronic mail, electronic news, file transfer etc.) with nodes or hosts outside of an office or organization, and these communications are now widely used.
In particular, in recent years, the use of the world's largest computer network called “Internet” has become very popular, and there are new computer businesses for connecting to the Internet and utilizing open information and services, or for providing information and services to external users who make accesses through the Internet. In addition, new technology is developed in relation to the use of the Internet.
Also, in conjunction with the spread of such networks, there are technological developments regarding the mobile computing. In the mobile computing, a user carries along a portable computer terminal and makes communications while moving over networks. In some cases, the user may change a location on a network while continuing the communication, so that there is a need for a scheme that manages a changing address of a mobile computer on a network during such a communication in order to route the communication content correctly.
In general, in the case of realizing the mobile computing, a router (home agent) for managing the visiting site information of the mobile computer is provided at a network (home network) to which the mobile computer belongs, and when the mobile computer is away from the home network, the mobile computer sends a registration message for indicating a current location to this home agent. When this registration message is received, the transmission of data destined to the mobile computer is realized via the home agent of the mobile computer, by carrying out the data routing control with respect to the mobile computer by encapsulating an IP packet destined to an original address of the mobile computer within a packet destined to a current location address of the mobile computer.
For example, in FIG. 1, this role is played by a home agent (HA) 105 when the mobile computer 102 that originally belongs to the home network 101a moves to another network 101b and carries out the communication with another computer (correspondent host: CH) 103 located within the other network 101c through the Internet 106. This is a scheme called Mobile IF which is currently in a process of being standardized by the mobile-IP working group of the IETF which is the standardizing organization for the Internet (see, IETF RFC 2002, IF mobility support (C. Perkins)).
The Mobile IP scheme aims at providing the mobility on the IP layer by continually using the same IP address even when a physical connection point on the network is changed. This mobility is superior to the so called nomadicity which simply enables a node to move from one network to another, in the following two respects: a loss of a session due to moving can be avoided, and an IP address can be used as a node identifier. For this reason, the Mobile IP is expected to be a protocol that can strongly support the mobile computing.
However, in the Mobile IP scheme, it is necessary to provide routers called home agents in order to support mobile nodes as described above. Also, in the Mobile IP scheme, there are cases involving triangular routes in the communications between a mobile node and the other host where a packet from the other host to the mobile node is transmitted via the home agent while a packet from the mobile node to the other host is transmitted without passing through the home agent.
These aspects of the Mobile IP scheme are expected to cause the following problems.
First, the home agent must be connected to a permanently connected network, and the mobile node cannot carry out any communications if the home agent falls to function properly. These facts weaken the robustness of the mobile communications.
Second, there is a mechanism called firewall which is indispensable in the current Internet environment, but the presence of a triangular route complicates the issue of firewall passing because the firewall cannot recognize a packet from the mobile node to the other host, for example.